This invention relates to a heating device for a fiber processing machine such as a carding machine or a roller card unit which produces a fiber web. At the output of the fiber processing machine calender rolls are provided for mechanically compressing (densifying) the web and further, a device is provided for binding the fibers to one another by heat.
The production of webs by roller card units or carding machines has always been of significant commercial importance which grew even further, particularly with the frequent use of natural fibers which require the roller card technology in case of thin webs. For strengthening the web, particularly in case of thin webs, a mixture of binding fibers with other chemical fibers or natural fibers has been processed, followed by a subsequent processing step in which the web, produced by the roller card, has been strengthened, for example, in a calender with heated rolls. The high degree of flexibility of the roller card process is a significant operational advantage. To increase the output of the machines it is a desideratum, on the one hand, to increase the operating width of the machines and, on the other hand, the output speed of the web. Since in case of width increase the costs for the machine and the feeder increase disproportionately to the widening, the latter has to be maintained within certain limits for economical reasons. Consequently, the development has been strongly concentrating on the increase of the output speed. Such increase, however, can occur in case of given web thicknesses only by increasing the web discharge delivery speeds. For this purpose, significant untapped possibilities may be found in the preparatory machines, roller card feeders and the roller cards themselves. Thus, a roller card is capable of producing fast-running thin webs and transferring them at high delivery speeds to the doffer. A drawback of this arrangement involves the subsequent guidance of the rapidly travelling webs downstream of the roller card to a successive processing machine, such as a thermobonding calender. To overcome these difficulties, the use of various additional devices has been suggested. According to one proposal, perforated belts have been provided which are placed under vacuum and advance the webs to the subsequent processing machine to ensure that the friction between the rapidly moved web and the surrounding air does not cause disturbances in the web. In such a solution, an exact coordination between the speed and strength of the vacuum in case of different web qualities and weights has been found to involve substantial difficulties. More particular and partially insurmountable difficulties, however, are encountered at the transfer locations between the delivery rolls of the roller card, the perforated belt and the feeding device in the calender, especially in case of high delivery speeds of 300 m/min and higher. These difficulties set technological limits which render significantly more difficult the starting, the normal operation and the stoppage which eventually lead to the result that only certain speeds can be set because above such speeds continuous disturbances are encountered. Lower output speeds, however, are uneconomical.
According to a known device, as disclosed in German Offenlegungsschrift (application published without examination) 36 17 862, a roller card unit is provided from which the web is introduced by means of conveying devices into a cross laying device and therefrom the web is further conveyed by additional advancing devices to a thermocalender in which the thermostrengthening is effected. The calender rolls have a low circumferential speed corresponding to the low delivery speed of the web. The transfers and directional changes of the web require a low speed to ensure that the web is not destroyed. It is a disadvantage of this arrangement that the production output is lowered.